core/host: userspace version fingerprint (sudo, polkit)

The host fingerprint now captures sudo + polkit versions at startup
so userspace-LPE modules can consult a single source of truth
instead of each popen-ing the relevant binary themselves on every
scan. Pack2theroot already queries PackageKit version via D-Bus
in-module, so PackageKit stays there for now.

core/host.h:
- new fields: char sudo_version[64], char polkit_version[64].
  Empty string when the tool isn't installed or version parse fails;
  modules should treat that as PRECOND_FAIL.
- documented next to has_systemd / has_dbus_system in the struct.

core/host.c:
- new populate_userspace_versions(h) called from
  skeletonkey_host_get() after the other populators.
- capture_first_line() helper runs a command via popen, grabs first
  stdout line, strips newline. Best-effort: failure leaves dst empty.
- extract_version_after_prefix() pulls the version token after a
  fixed prefix string ('Sudo version', 'pkexec version'), handling
  the colon/space variants.
- skeletonkey_host_print_banner() gained a third line when either
  version is non-empty:
    [*] userspace: sudo=1.9.17p2  polkit=-

Module migration (graceful fallback pattern — modules still work
without ctx->host populated):
- sudo_samedit detect: if ctx->host->sudo_version is set, skip the
  popen and synthesize a 'Sudo version <X>' line for the existing
  parser. Falls back to the original find_sudo + popen path if the
  host fingerprint didn't capture a version.
- sudoedit_editor detect: same pattern — host fingerprint sudo_version
  takes precedence over the local get_sudo_version popen.

tests/test_detect.c additions (2 new cases, 33 → 35):
- h_vuln_sudo  fingerprint (sudo_version='1.8.31', kernel 5.15) —
  asserts sudo_samedit reports VULNERABLE via the host-provided
  version string.
- h_fixed_sudo fingerprint (sudo_version='1.9.13p1', kernel 6.12) —
  asserts sudo_samedit reports OK on a patched sudo.

This is the first test pair to cover the *vulnerable* path of a
module rather than just precondition gates — proves the
version-parsing logic itself, not only the short-circuits.

Verification: 35/35 pass on Linux. macOS banner shows
'userspace: sudo=1.9.17p2 polkit=-' as the dev box has Homebrew
sudo but no polkit.

core/host.h

@@ -70,6 +70,16 @@ struct skeletonkey_host {
 	bool has_systemd;                 /* /run/systemd/system exists */
 	bool has_dbus_system;             /* /run/dbus/system_bus_socket exists */
 
+	/* ── userspace component versions ─────────────────────────
+	 * Parsed once at startup via popen() of the relevant binary's
+	 * --version output. Empty string ("") means "tool not installed
+	 * or version parse failed" — modules should treat that as
+	 * PRECOND_FAIL (no exploit target). The exact format mirrors
+	 * what the tool prints (`Sudo version 1.9.5p2`, `pkexec version
+	 * 0.105`, …); modules do their own range parsing. */
+	char sudo_version[64];            /* "1.9.13p1" or "" */
+	char polkit_version[64];          /* "0.105" or "126" or "" */
+
 	/* Informational: the SKELETONKEY component that populated this
 	 * snapshot (for log/JSON output). */
 	const char *probe_source;